<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
		<script>
			
			
			sum();
			
			function sum(){
				alert(a);
				var a = 2;
				alert(a);
			}
			var a = 1;
			alert(a);
			
			
		</script>
	</body>
</html>
